Impact of physiological parameters on the parotid gland fat fraction in a normal population

www.nature.com/scientificreports OPEN Impact of physiological parameters on the parotid gland fat fraction in a normal population Ari Lee , Yoon Joo Choi , Kug Jin Jeon , Sang‑Sun Han  & Chena Lee * Quantifying physiological fat tissue in the organs is important to further assess the organ’s pathologic status. This study aimed to investigate the impact of body mass index (BMI), age, and sex on the fat fraction of normal parotid glands. Patients undergoing magnetic resonance imaging (MRI) of iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL-IQ) due to non-salivary gland-related disease were reviewed. Clinical information of individual patients was categorized into groups based on BMI (under/normal/overweight), age (age I/age II/age III), and sex (female/male) and an inter-group comparison of the fat fraction values of both parotid glands was conducted. Overall, in the 626 parotid glands analyzed, the fat fraction of the gland was 35.80%. The mean fat fraction value increased with BMI (30.23%, 35.74%, and 46.61% in the underweight, normal and overweight groups, respectively [p < 0.01]) and age (32.42%, 36.20%, and 41.94% in the age I, II, and III groups, respectively [p < 0.01]). The fat content of normal parotid glands varies significantly depending on the body mass and age regardless of sex. Therefore, the patient’s age and body mass should be considered when evaluating fatty change in the parotid glands in imaging results. The parenchyma of the salivary gland is composed of secretory and connective t issues1. As gland dysfunction progresses, histological components change. Prominent changes can be observed when the increased proportion of adipose tissue displaces the acinar cells, the secretory part of the gland1,2. Thus, the adipose tissue contained in the glands is considered an important indicator of gland dysfunction3–6. As the fat fraction is considered an indicator of gland function, different measurement methods using various imaging techniques have been i ntroduced7–9. In addition, the internal body organs are continually changing their tissue composition according to physiological conditions10. Thus, many researchers have studied the fat fraction alteration of organs, such as the liver or bone marrow, according to physiological factors including age, sex, or body mass11–13. However, few studies have focused on the fat fractional changes in the salivary glands related to physiological factors. Studies on the salivary gland are not exhaustive, and they have revealed a weak to moderate linear correlation between physiological factors and the fat fraction until recently14,15. Quantification of alteration in the fat fraction of the salivary gland from baseline is needed prior to studying gland dysfunction. Fat quantification can be performed based on various techniques of magnetic resonance imaging (MRI). Among them, Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation (IDEAL-IQ) is known as a reliable and precise method for fat q uantification16. Basically, this method uses magnetic resonance spectroscopy and measures the proportion of metabolites, including lipid and water, according to their different resonance frequency in the magnetic field. The iterative least-squares decomposition algorithm calculates the fat and water value of the individual pixels in the entire image and produces a fat fraction map image17. The IDEAL-IQ is a recently developed method that separates the water-fat signal and simultaneously estimates T2* based on a multiecho chemical shift. The technique is known to calculate fat, which has multiple spectral peaks, more accurately18. In addition, a previous study reported the successful measurement of fat saturation in the head and neck with metal artifacts having little effect on the MR i mage14. Currently, this method is widely applied clinically and in the research field to analyze the liver or bone marrow of the proximal f emur13,19,20. However, few researchers have used this method to study the salivary gland fat fraction14,15. It is necessary to explore the fat fractional change in normal parotid glands according to physiological parameters in a large population. Therefore, this study aimed to investigate the impact of body mass, age, and sex on the fat fraction of the normally functioning parotid gland. In addition, the difference in the fat content of the gland according to individual physiological factors was suggested using the IDEAL-IQ technique. Department of Oral and Maxillofacial Radiology, Yonsei University College of Dentistry, 50‑1 Yonsei‑ro Seodaemun‑gu, Seoul 03722, Republic of Korea. *email: Scientific Reports | (2023) 13:990 | https://doi.org/10.1038/s41598-023-28193-z 1 Vol.:(0123456789) www.nature.com/scientificreports/ Methods This study was approved by the institutional review board (IRB) of Yonsei University Dental Hospital (No. 2-2021-0058) and was conducted in accordance with the relevant guidelines and ethical regulations. Due to the retrospective aspect of this study, the need for informed consent was waived by the by the IRB of Yonsei University Dental Hospital. Study population. Patients who underwent MRI examination from July to December 2020 at our institu- tion were included in the study. A thorough chart review was performed to collect general clinical information; details on age, sex, body weight, and height; and current or previous history of any compromised disease. The exclusion criteria were as follows: patients (i) diagnosed with salivary gland tumors, sialadenitis, or autoimmune diseases, (ii) who underwent radiation therapy due to head and neck cancer or symptoms of oral dryness, (iii) without metabolic diseases such as hypertension and diabetes, and (iv) for whom it was difficult to evaluate and measure owing to degraded image quality caused by artifact. The IDEAL-IQ images covering the complete volume of the parotid gland without any imaging errors were included in this study. The process of selecting the patients has been explained in detail in a flow chart (Fig. 1). Scan parameters. All MRI scans were acquired using a 3.0 T scanner (Pioneer; GE Healthcare, Wauke- sha, WI, USA) with a 16-channel flex large coil. IDEAL-IQ and T2-weighted images in the axial view were included in this study. The imaging parameters of IDEAL-IQ were as follows: echo time, 1.00, 2.04, 3.08, 4.12, 5.16, 6.20 ms; echo train length, 3; repetition time, 10.52 to 10.63 ms; bandwidth, 868.047 kHz; NEX, 1.0; field of view, 240 × 240 mm; slice thickness, 4.0 mm; scan time, 1 min. flip angle, 4°; and matrix, 160 × 160. The imaging parameters of T2-weighted image were as follows: echo time, 85 ms; echo train length, 9; repetition time, 3100 ms; bandwidth, 83.33 kHz; NEX, 1.0; field of view, 230 × 230 mm; slice thickness, 4.0 mm; scan time, 2:17 min; flip angle, 111; and matrix, 380 × 320. Physiological parameters. Body mass in (...truncated)